Federer loses to Del Potro but will face Murray

Roger Federer will face Andy Murray in the semi-finals of the ATP World Tour Finals despite his loss to Juan Martin Del Potro on Saturday.

A victory for Federer - who was already assured a place in the last four regardless of the result - would have booked the Swiss a date with Murray. Likewise, a straight-sets win for Del Potro would have seen the Argentine meet the home favourite.

However, Del Potro overcame the former world No. 1 7-6(3) 4-6 6-3 at London's O2 Arena, meaning top spot in Group B would not be decided until the outcome of the evening encounter between Janko Tipsarevic and David Ferrer.

A Ferrer win would see Federer face Murray and the Spaniard battled back from the loss of the first set to claim victory.

Earlier in the day and there was less riding on the match for Federer than his rival, but he did have a proud record to protect as he entered the contest riding a 12-match win streak in the competition. Federer is also the defending champion, but the difference between facing Murray and Djokovic in a semi-final is marginal on current form.

Nevertheless, both players made focused, solid starts, holding serve without fuss until the eighth game - when Federer converted an easy smash for 15-40 on the Del Potro delivery. It proved a false down as Del Potro emerged unscathed, saving three break chances en route to 4-4.

Federer's overall career record against the Argentine is extremely impressive, winning 13 or 16 previous meetings, and six of seven in 2012. However, Del Potro's solitary triumph came in their most recent meeting in Basel, and he also pushed Federer to 19-17 in the third set of their Olympic clash on English soil during the summer.

The pair have a tendency to bring out the best in each other, and that was clearly evident during one point of game nine, which included a lob, a hot-dog, a backhand smash and a cute angled volley - won by Federer. However, Del Potro forced the tiebreaker at the end of the first set, before he tore into Federer with a bunch of meaty forehands to establish a one-set advantage.

The momentum stayed with Del Potro for all of five minutes as Federer came out firing at the start of the second, rifling an array of shots at the baseline to break to love. He quickly advanced to 3-1 with a series of simple service holds, and one topspin forehand winner deep to the baseline testified to the groove the Swiss had found.

It seemed only right that Federer should level - having dropped five points on serve in the set, and he did so with ease to make it one set apiece with Del Potro yet to create a single break chance in the match.

That statistic quickly changed at the start of the third, Del Potro turning to his less favoured backhand side to hit a winner to break in Federer's opening service game. He then accelerated out to 3-0 with the crowd delighted at the quality on show.

Now it was Del Potro dominant on serve as he advanced to 4-1 without dropping a point behind his own delivery. Federer's frustration was clear as he let out an angry yell mid-set, but defeat made little difference to the Swiss as Ferrer beat Tipsarevic to set up the clash with Murray.